The present invention relates generally to ground fault safety devices and more specifically to appliance leakage current interrupters.
It is well known for electrical appliances, such as hair dryers, to draw electrical power through connection to a power source, such as an electrical outlet. Specifically, the electrical appliance (which serves as the load of the electrical system) is connected to the power source by a pair of current-carrying wires. The pair of current-carrying wires typically include a hot wire and a neutral wire, the pair of wires having equal but opposite magnitudes under normal conditions.
On occasion, the electrical system may experience a ground fault condition while the load is connected to the power supply. A ground fault condition occurs when the differential between the values of the currents of the two wires exceeds a predetermined value. Often a ground fault will occur if the hot line becomes inadvertently grounded. A ground fault condition can result in a loss of power to the electrical appliance because current is unable to flow to the load. As a consequence, an excessive amount of current tends to flow into the ground conductor of the electrical system which, in turn, creates dangerous voltage levels at points in the circuit that should be at ground potential. This condition can result in potentially dangerous electrical shocks, which could seriously injure an individual.
Accordingly, ground fault safety devices are commonly employed in such electrical systems to eliminate ground fault conditions. One type of ground fault safety device is the ground fault circuit interrupter (GFCI). Another type of ground fault safety device is the appliance leakage current interrupter (ALCI). Ground fault circuit interrupters are used to eliminate ground fault conditions as well as grounded neutral conditions, whereas appliance leakage current interrupter are used only to eliminate ground fault conditions. Both types of ground fault safety devices prevent ground fault conditions from occurring by opening the electric circuit upon the detection of a ground fault condition in the pair of wires.
It is known to incorporate GFCI's and ALCI's into electrical plugs, electrical switches and electrical receptacles.
U.S. Pat. No. 5,177,657 to M. Baer et al. discloses of a ground fault interrupter circuit with an electronic latch. The ground fault interrupter circuit interrupts the flow of current to a pair of lines extending between a source of power and a load. The ground fault interrupter circuit includes a circuit breaker comprising a normally open switch located in one or both of the lines, a relay circuit for selectively closing the normally open switch, an electronic latch circuit operable in first and second bi-stable states and a fault sensing circuit for sensing the presence of a fault condition in at least one of the lines. The electronic latch circuit causes the relay circuit to close the normally open switch and maintain the normally open switch in its closed position when the electronic latch circuit is in the first bi-stable state. The electronic latch circuit also causes the relay circuit to permit the normally open switch to return to its normally open condition when the latch circuit is in its second bi-stable state. A fault sensing circuit senses the presence of a fault condition in at least one of the lines and causes the electronic latch circuit to latch in its second state upon detection of the fault condition.
One well known and commonly used ALCI is made by Tower Manufacturing Corporation and is shown U.S. Design Pat. No. 356,066 to C. P. Rao et al. This ALCI includes a fault detection circuit to detect the presence of a ground fault condition. The fault detection circuit includes a five layered transformer which monitors the current differential between the hot and neutral lines. The fault detection circuit also includes an integrated circuit (IC) chip which generates a output fault signal whenever the imbalance between the currents in the hot and neutral lines exceeds a predetermined value. The output fault signal is sent to a relay circuit which is coupled to a pair of switches, one switch being located in the hot line and one switch being located in the neutral line. When the magnitude of the output fault signal generated by the transformer exceeds a predetermined value, the IC chip applies power to the relay circuit which causes the pair of switches to open the hot and neutral lines. The IC chip used in the circuit is Raytheon Corporation chip number RV4145.
The circuit of the ALCI described above is commonly mounted within a generally rectangular housing having a top, a bottom, a front end and a rear end. The housing is attached to the appliance by an electrical cord which extends into the housing from the rear end. A pair of prongs (blades) typically extend out from the bottom of the housing and are sized, shaped and spaced away from each other so that they can be inserted into the sockets of an electrical outlet, thus making contact and closing the circuit.
The circuit components of the above identified ALCI are typically through-hole mounted on one side of a single-sided circuit board which is positioned within the housing and all the conductive connection lines and pads are soldered on the other side of the circuit board. In particular, it should be noted that the IC chip is mounted on the first side of the circuit board through plated-through hole technology.
In U.S. Pat. No. 5,198,955 to Wilner, there is disclosed a miniature circuit interrupter for interruption of a primary circuit, the circuit interrupter formed or molded with a plug, connector or the like, the plug or connector being non-serviceable and the circuit interrupter therein being sealed and watertight.
Another patent of interest is U.S. Pat. No. 4,567,544 to Ronemus et al.